This invention relates generally to electrical protective equipment and, more particularly, to fused cutouts.
Fused cutouts are devices used extensively in electrical distribution circuits, such as for line sectionalizing. They are used for opening a relatively high current circuit, usually 100 amperes or more, upon an overload with means for facilitating replacement of the fuse and reclosing on a distribution line in the field. A cutout mechanically and electrically supports a fuse device in relation to a distribution line.
For background refer to FIGS. 1 and 2 which illustrate a widely used type of fused cutout. The cutout has an elongated, solid porcelain insulator 10. The insulator 10 has top and bottom rods 11 and 12 extending from it laterally as well as a back bracket 14, the latter being to secure the device on a pole or other fixed support. Each of the rods 11 and 12 supports an assembly for removably holding and making electrical contact with the ends of a fuse holder 16 containing a fuse link. The fuse holder 16 will not be described herein other than that it is characteristic of the fuse devices used with cutouts that the upper and lower contacts 18 and 20 are in pressure conductive engagement with fuse support elements affixed to the insulator.
In FIGS. 1 and 2, the support elements include a first top bracket 22 and a top hood 24 affixed to the top rod 11. A second top bracket 26 extends upwardly from the top hood 24 and is joined to it by two rivets 60. A guide post 28 extends vertically through the structure including the top hood and the extremity of the first top bracket 22. There are also contact elements 30 having an upper extremity 30a that is attached by rivets 60 just under the top bracket 26 and top hood 24 and a lower portion 30b supported on the first bracket between which a spring is provided that biases the portions 30a and 30b of the contact element 30 apart for the purpose of maintaining downward pressure on the bottom portion 30b of the contact element within a notch 30c of which are engaged the upper contact pegs 18 of the fuse holder 16. FIG. 2 shows the general orientation of the contact elements 30 attached by rivets 60 to bracket 26.
The second top bracket 26 holds the line terminal 34 for connecting one end of the cutout to a distribution line and that bracket is of highly conductive material such as copper and also must be sufficiently strong to support the terminal such as having a thickness of about 0.125 inch. The conductive path proceeds from the line terminal 34 through the bracket 26 to a riveted joint. Bracket 26 conductively engages the top portion 30a of the contact element 30 at the rivet 60 with the head of the staked rivet holding the elements 26 and 30a together. The top and bottom portions 30a and 30b of the contact element 30 are joined by rivets 33 and 30b is guided by post 28 as 30b is raised by the contact pegs 18 to permit 18 to reach 30c.
At the bottom of the structure, the rod 12 supports a bottom hood 36 and also a bottom support casting 42 to which the bottom line terminal 40 is attached by bolt 51. The bottom line terminal bracket 40, like the top line terminal bracket 26, is both highly conductive and mechanically strong. The bottom support casting 42 has fastened to it a contact element 44 which is highly conductive flexible copper strip for contacting the fuse holder contacts 20 at the lower end of the fuse holder 16. Contact element 44 is one of a pair of such contact elements configured similarly to contact elements 30 at the upper end.
A further description of cutouts of the character of that depicted in FIGS. 1 and 2 is contained in Descriptive Bulletin 38-651 of Westinghouse Electric Corp., July 1977, which is herein incorporated by reference.
The cutout as shown in FIG. 1 has been successful in performance. It is however desirable to increase the reliability of the device so that it can serve a longer life and also to reduce its costs. We do so by changing to a design, to be described in greater detail hereinafter, that avoids the need for some of the elements at both the top and bottom ends of the device that require both high conductivity and high mechanical strength. Only a single conductive element at each end is required and it does not need mechanical support capability. It is seen from FIG. 1 that at each of the ends of the device the conductive elements have to be mechanically joined in two places. At the upper end, the line terminal bracket 26 and the top contact portion 30a are joined at the rivet 60. Also, the contact support portions 30a and 30b are joined by a rivet or the like 33. At the lower end, one joint is between elements 44 and 42 where 44 is riveted to 42 and another is between 42 and 40. These joints are vulnerable to becoming loose or being loose from improper assembly and are completely eliminated as a source of potential problems in the design in accordance with this invention.
In the new design a single conductive element extends from the line terminal to the fuse contacts at each end of the device. We have found that the purposes of the invention can be very satisfactorily achieved by avoiding reliance on the conductive element for any mechanical support and reconfiguring the design so as to permit a continuous conductive element, such as of copper while the other elements may be of steel or the like, to extend from the line terminals to the fuse contacts.